In general, molds included in an injection molding machine, are formed with a movable mold and a fixed mold, and they are supported by a mold clamping device. The mold clamping device includes a fixed platen whose position is fixed and a movable platen whose position is varied, and the fixed mold and the movable mold are respectively attached to the fixed platen and the movable platen with a predetermined clamp portion. Incidentally, although a bolt and nut is widely known as the clamp portion, an attaching operation (clamp operation) is complicated, and thus it is a disadvantage because of which it is not easy to be able to achieve automation. Hence, a clamp portion, apart from the bolt and nut that facilitates the automation of the clamp operation, is also practically used.
Conventionally, as the above-described clamp portion that facilitates the automation, a fluid pressure clamp disclosed in patent literature 1 and a magnetic fixing device disclosed in patent literature 2 are known. However, in the conventional clamp portion that does not use the bolt and nut, although it is easy to switch between a clamp state (ON) and a clamp cancellation state (OFF) with a button operation, the mold attachment surfaces of a movable platen and a fixed platen are perpendicular surfaces (vertical surfaces), and in the case of a multi-color molding injection molding machine that sequentially switches a plurality of sets of molds to perform molding, it cannot necessarily be said that the attaching operation is facilitated. In other words, when the bolt and nut is manually operated to adjust the position of the mold, the bolt and nut is loosened sensuously by an operator such that the mold is prevented from being dropped, and in such a state, it is possible to finely adjust the position, whereas when the clamping is performed with the clamp portion that does not use the bolt and nut, it is possible to easily perform the clamp operation itself but it is impossible to easily adjust the position of the mold.
On the other hand, a mold clamping method that can easily and reliably clamp and locate a mold and, in particular, is preferably used when a plurality of molds included in a multi-color molding injection molding machine, or the like, are attached to a mold clamping device, is also known. In this clamping method, the following steps are provided: a first step in which a movable platen is brought into a mold open state and a clamper is brought into a clamp cancellation state, the mold is fitted between mold attachment surfaces, the movable platen is moved to a mold clamping position and thereafter all clampers are switched to a clamp state; a second step in which the movable platen is brought into the mold open state and thereafter a rotary platen is rotated to switch the position of a movable mold; a third step in which when the movable platen is moved in a mold closing direction and reaches a previously-set predetermined cancellation setting position, a clamper, in one of the movable mold and a fixed mold opposite each other, is switched to the clamp cancellation state; and a fourth step in which the movable platen is moved to the mold clamping position and thereafter the clamper that has been brought into the clamp cancellation state in the third step is switched to the clamp state.